The light-sensitive materials for photo-mechanical process are light-sensitive materials used in a photographic photo-mechanical process step in the printing industry, such as for converting a continuous light-shade image into a dot image or photo-graphing a line drawing, etc.
When such light-sensitive materials for photo-mechanical process are used for making printing plates, a treatment called reduction treatment is frequently conducted. This treatment is performed in order to obtain delicate reproduction of tone or satisfy artistic expression of the images adapting to printing characteristics, by which fine correction of images is carried out partially or completely. The corrections may include reduction of the area of dots or widening or narrowing of the width of a line drawing.
Therefore, aptitude for reduction treatment is a very important property in light-sensitive materials for photo-mechanical process.
When carrying out reduction treatment of light-sensitive materials for photo-mechanical process having dot images or line drawing images formed by exposure and development processing, it has been known to use a method which comprises contacting metal silver forming the dot images or line drawing images with a reducer. Various kinds of reducers are known. For example, reducers using a reducing component such as a permanganate, a ferric salt, a cerium (IV) salt, a ferricyanide, a bichromate or a persulfate, etc., have been described in Mees, The Theory of the Photographic Process, pages 738-739 (1954, published by Macmillan Co.).
Reduction treatment is a treatment comprising oxidizing silver images by a reducer to dissolve them. Accordingly, when dot images are subjected to reduction treatment, the decrease in dot area is achieved along with a decrease in the blank density of the dots. Therefore, the extent to which dot images can be corrected by the reduction treatment is restricted by a degree of the decrease in blank density of each dot which occurs together with the decrease in dot area. In other words, a measure of the extent to which dot image can be corrected can be represented by a reduction of dot area while maintaining the black density of each dot at a specified value or more.
In the present specification, the term "reduction width" means a decrease in dot area from the dot area before the reduction treatment when the black density of the dots is decreased by the reduction treatment to the lowest value necessary for the photographic photo-mechanical process step. Thus, the wider the reduction which is, the higher the reduction treatment aptitude is.
A method for improving reduction treatment aptitude is described, for example, in Japanese Patent Application (OPI) No. 68419/77. A mercapto compound is used for the reduction treatment. However, the reducer is specific and difficult to use, because its reduction rate is different from that of conventionally used reducers. Further, it is possible to widen the reduction width resulting in the improvement in reduction treatment aptitude while increasing the density due to increase in the covering power by softening the emulsion membrane. However, the required film strength cannot be obtained by this method.
The most effective method for improving the reduction treatment aptitude due to widening the reduction width is increasing the silver content for forming the images. This method is effective because the ability to correct images by the reduction treatment is generally increased when there is a greater amount of silver in the silver images per unit area, where, as described above, the reduction treatment comprises oxidizing silver images by a reducer to dissolve them. Therefore, the reduction width can be increased when a coating amount of silver halide per unit area in the light-sensitive material for photo-mechanical process to be used is increased. However, since silver is very expensive and rare, increasing the coating amount of silver is not preferred in view of the cost of the light-sensitive materials for photo-mechanical process and economy of resources.
Accordingly, it is an important subject in this field to produce a light-sensitive material for photo-mechanical process having the required properties while using silver in an amount as low as possible.
As a result of extensive investigations relating to improving such problems, it has been found that widening the reduction width and thus remarkable improvement in the reduction treatment aptitude can be achieved where the hardness of the light-insensitive upper layer is increased utilizing a hardening technique capable of controlling the hardness of the light-insensitive upper layer and that of the silver halide emulsion layer, separately (i.e., selective hardening technique of the coating layers) as described in Japanese Patent Application (OPI) No. 42039/83 (corresponding to British Pat. No. 2,108,605A).
When dealing with a multilayer coating material, if the upper layer is hardened so as to have a hardness higher than that of the lower layer, network patterns called "reticulation" occur, when high temperature treatment with an exhausted processing solution is utilized (edited by R. J. Cox, Jojo et al., Photographic Gelatin, pages 49-61 (1972), Academic Press). Accordingly, it is desirable to prevent the occurrence of reticulation for the light-sensitive material for photo-mechanical process in which the reduction treatment aptitude is improved utilizing the selective hardening technique of the coating layers.